An air bag module intended for installation in a vehicle, in particular a front air bag module, consists of an air bag, a receiving and retaining element to receive and hold an air bag, and an inflator to fill the air bag. In this connection, a gas generator is frequently used as an inflator, in particular, a hot gas generator in which a pyrotechnic charge that on ignition produces a large quantity of hot gas which fills the air bag.
Originally, large parts of the receiving and retaining element, namely in particular the housing, a possibly provided retaining ring, and a possibly provided diffuser, were made of metal. In the meantime, for cost and weight reasons, many parts which were originally made of metal are now made of plastic, and it is possible to provide plastics and geometries which meet the current mechanical and thermal requirements. Small and very hot gas generators are, however, increasingly being developed which, in particular, have the advantage of a low weight. It has turned out in laboratory tests that the temperatures which are reached with the use of such generators may give rise to problems if certain components of the receiving and retaining elements are made of the thermoplastics that have been used so far. The following components or sections of the receiving and retaining elements can, in particular, be affected: the housing floor/base plate, especially in the area in which the gas generator is held by means of its flange; any possibly provided retainer ring; any possibly provided diffuser; any possibly provided deflector, (flame retardant wall).
In view of the foregoing, the object of the present invention is to provide an air bag module in which temperature-exposed components can also be made of plastic when very hot gas generators are used.
This object is attained by an air bag module described herein, and a process, with which such an air bag module can be manufactured, is also described.
In order to solve the design challenges mentioned above, it would be basically possible to use high temperature resistant plastics, in particular, high-temperature resistant polyamides. That would, however, entail critical disadvantages since, on the one hand, such materials have a low notched impact strength and, in addition, high tool temperatures will also be required during injection molding. This, on the one hand, increases the energy consumption during injection molding and also reduces the service life of the tools used. This would lead to a significant increase in the cost of the air bag module, which are reasons why this approach has not been adopted in the present invention. Instead, according to the present invention, at least one component of the air bag module consisting of plastic is radiation crosslinked after shaping. In the process, the plastic—which, in particular, is a thermoplastic—can have a so-called cross-linking activator. The production, in particular the injection molding, requires no special process; in particular, common tools with common temperature control may be used. In a process step which preferentially is interposed between the production steps, in particular, injection molding of this part, and the final assembly of the air bag module, the component is exposed to ionizing radiation, namely, in particular, to gamma or beta radiation, whereby the plastic material is crosslinked. This crosslinking is also called radiation crosslinking. This crosslinking (radiation crosslinking) also results, among other things, in that the thermal stability, in particular the short-term thermal stability, of the plastic definitely increases compared to its non-crosslinked original condition. Thus, for example, the thermal stability of PA-6.6 GF 30 increases from about 250° C. to about 360° C. and that of PA-6 GF 30 from about 200° C. to about 350° C.
The required irradiation is not a very expensive process step and can, in particular, take place in that a large number of components to be irradiated are irradiated in a large container lying loose therein. Such a process is known, for example, from the production of plugs, namely when plastic encapsulations of plug connectors are radiation crosslinked in order to withstand high soldering temperatures.
The main application of the invention could lie in the field described above, namely with the objective of making components of a receiving and retaining element more temperature-resistant. It has turned out, however, that the invention can also be applied in the area of air bag modules. It is thus, for example, possible to radiation crosslink at least one section of the air bag, in particular at least one reinforcing layer surrounding the inflation inlet in order to increase its thermal stability. According to the current state of knowledge, however, radiation crosslinking sections or elements of the air bag module only makes sense if this element or section consists of a laminate, since in a fabric the filaments are too thin for radiation crosslinking. It can, in particular, be very useful to use at least one radiation crosslinked laminate in the area of the inflation inlet, since a flame retardant can be provided very cost-effectively in this manner, which can make the use of a silicon coating unnecessary, or result in an even higher thermal stability in conjunction with a silicone coating. The volume of exhaust gas, which can be generated by scorching of the air bag fabric, can be reduced in this way.
A completely different application can consist of selectively radiation crosslinking the predetermined breaking lines of the housing cover, since radiation crosslinking not only leads to an increase of the thermal stability but also to an increase of the brittleness which can have a favorable effect on the controlled opening behavior of the exits doors.